<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script src="./lib/vue-2.4.0.js"></script>
    <link rel="stylesheet" href="./lib/bootstrap-3.3.7.css">
</head>
<body>
    <div id="app">
        
        <input type="text" v-model='firstname' >+
        <input type="text" v-model='lastname' >=
        <input type="text" v-model='fullname'>

    </div>
    <script>
        var vm=new Vue({
            el:"#app",
            data:{
                firstname: '',
                lastname: '',
                fullname: '',

            },
            methods: { },
            watch: {//使用这个属性，可以监听 data 中指定的数据变化。然后触发这个 watch中对应的function函数
                firstname: function(newVal){
                    // this.fullname = this .firstname + '-' + this.lastname
                    this.fullname = newVal + '-' + this.lastname
                },
                lastname: function(newVal){
                    // this.fullname = this .firstname + '-' + this.lastname
                    this.fullname = this.firstname + '-' +  newVal
                }
            },
        })
    </script>
</body>
</html>